Electrical tuned circuit



Dec. 2l, 1937; D. E. oDoNovAN 2,102,805

ELECTRICAL TUNED CIRCUIT Filed Sept. 7, 1955 -2 Sheets-Sheet l /7 y f6 f5 E@ QB E *N* b S Qq *l "g 3500 g 'g sooo E 24 300 a 2500 FULL 20 250 TOR 0000/070 (wwwa/m0) CL 0g @0 gf 000 DANIEL E.o'DoNo\/AN BY WMM ATTORNEY.

Deu 21, 1937. D. E. @DONOVAN 2,102,805

ELImTRICAL,` TUNED CIRCUIT Filed Sepvt. 7, 1935 2 Sheets-Sheet 2 INYENTOR, DANIEL E. ODONOVAN ATTORNEY,

Patented Dec. `21, 1937 PATENT OFFICE Y ,2,102,805 v VELECTRICAL TUNED CIRCUIT Daniel Edward ODonovan, Chelmsford, England,

assignor to Radio Corporation of America, a.

corporation of Delaware Application September 7,' 1935,Serial No. 39,583

l In Great Britain July 21, 1934 6 Claims.

This invention relates to electrical tuned AcircuitV arrangements and has forv itsobject to provide improved mechanical constructions of electrical tuned circuits of the parallel type, i. e. of the type in which the inductive'is `in parallel with the capacitive portion. y

Although not limited to its application thereto, the invention is particularly advantageous for and is primarily intended vfor application to so-called rejector circuits rfor rejecting unclesired harmonics in Yradio transmitters.

The practical desiderata of tuned circuit arrangements suitable for use for the above and similar purposes includeA that they shall be simple and cheap to construct; easy to accommodate; inherently self-screening, i. e., of YSuch construction as to give rise to a minimum of -ex- -t'ernal disturbing fields; adjustableas to natural frequency over a considerable range; of low inductance so that voltage drop and power losses at the fundamental wave length of the transmitter in question (i. e. the wave length which is not to be rejected) shall be low; and of low high frequency resistance, and therefore of high harmonic attenuation.

The present invention provides tuned circuit arrangements which satisfy the -above desiderata and have the advantages of low radiation, connection, contact, and inductance losses.

According to this invention, Va tuned circuit of the parallel typecomprises, an outer tubular conductor, a second conductor positioned within `-saidouter conductor, 'one or more flxedcondensers connected between said inner-and' outer conductors and a bridge member sldably mounted with reference to said conductors and adapted to contact vvith'bothI of them. With this arrangement, movement of the bridge member longitudinally of the two conductors variesthe inductance-Which vis provided by. Vsaid conductors-in shunt with said condenser or condensers. v

The invention is Villustrated in and further explained in connection with the accompanying drawings, in which:

Figs. 1 to 4 show a preferred way of carrying out the said invention, and Fig. 5 is a set of graphs. In the drawings:y Fig. l is a-sectional elevation, Fig. 2 a right end view looking towards the handle, Fig. 3 a left or opposite end view, and

l Fig. 4 a part plan showing the handle link.

Referring to the drawings, the tuned circuit arrangement therein shown comprises a straight circular tubular outer conductor'l of copper- Vvfor `example a copper tube of about 7 internal diameter and about '1' long--asecond or inner straight tubular copper conductor 2, also about 7' long but of about 2 external diameter, the

inner conductor being arranged Within and concentric with the outer conductor, a piston like `member having a central hole adapted to fit over andV contact with the inner conductor and being of such size that its periphery .contacts with the inner face of the outer conducto-r, and a plurality;

'oifixed condensers 3 connected betweenthe two conductors I, 2, at or near one end of the whole tubular conductor structure. At the condenser end of the structure the inner conductor V2 may be formed with a hexagonal outer surfacerv (or a hexagonal nut may be screwed thereon) and the fixed condensers may be arranged'radially between the two conductors, one terminal end of each condenser-assuming there are sixresting on and contacting with one of the flats of the hexagon on the inner conductor, the other terminal ends of the condensers being bolted or otherwise fixed to theY outer conductor so that the condensers are in parallel with one another and connected between the inner and outer con-5.5;-

ductors. In the illustrated arrangement, however, the Ycondensers are in a unit assembly comprising a hexagon-ended plug 2| ,which ts into the end of the tube 2, which is slotted at 22',l the cylindrical portion of the plug being grippedvr by the action of band clamps 23 about the slotted tube end. The terminal lead 3a of each condenser 3 is pressed against a hexagonal face on the plug and-(so as to be clamped beweenisaid surface and the condenser) by means of a bolt,

4 and plate 5 and the other terminal 3b is clamped as shown at 6 against a ange 24ar formed on the housing 24 which surrounds the condenser assembly and receives the bolts 4.

The terminals aref markled 25 and 26.- Thai, major portion of the lengths of the conductors' are of circular section and the piston,r which has a contacting member 1 which is preferably of copper, is slidably arranged and is of suiiicient length to make good electrical contactboth with inner and outer conductors. The piston com" prises two plates 8,V 9, which are parallel to one another, the plate 8 being recessed at 8a toreceive the ends of the contacting member which is of dished annular form. Screwed into the., plate 8 are studs l0, the ends of which pass split as at 1a. to facilitate expansion andis off will be appreciated, that` portion of the lengths of the inner and outer springy material. As

conductors between the condensers and the piston, together with the piston itself, constitute a single turn inductance which will give substantially zero external iield and which is in parallel with the capacity provided by the condensers. By sliding the piston longitudinally this inductance can be varied. A plurality of ranges of natural frequency .can be obtained simply by changing the number and/or size of the shunt condensers. In practice the shunt capacity is chosen at such value that the desired natural frequency is obtained when the piston is -`about six feet from the condensers. Fine' adjustment is then accomplished by moving the piston by means of the handle I3, which is insulated so as to enable this adjustment to be madewhen the apparatus is in operation in a transmitter. The handle I3 is on the end of a lever system I4 pivoted at l5 to a link system I6 in turn pivoted at II, the strips comprised in the lever system I4 being bowed out at Ma to surround a sleeve I8 which is fast with the piston andwhich is engaged by means of pins I9 carried in the bowed out strips and which enter holes 20 in the sleeve I8. As will be seen, the handle and lever mechanism illustrated enables a very :tine adjustment to be readily made. There is a plurality of holes 20 spaced along the sleeve I3 so that coarse adjustment of piston position can be obtained by selecting the desired hole 20.

The curves A, B, C of Fig. 5 show practical results which have been achieved with an -arrangement such as that illustrated and which tunes at 694.5 metres with the piston at about 6 from the condensers. Curves A show three resonance curves (ordinates-impedance against abscissae-wavelengths) for three positions of the piston; curve B shows impedance (ordinates) against displacements of the piston in inches (abscissae) on either side of a position (O) at which the rejector tunes to 694 metres (this is with the piston at about six feet from the condensers); and curve C shows position of piston (ordinates) against tuning wave length (abcissae). Curve D is a curve of impedance in ohms (ordinates) plotted against wave length (in metres) for a rejector in accordance with this invention and having an effective length of six feet. This curve shows the efficiency of appa- Y ratus in accordance with this invention when used or tuned rejectcr purposes at short wave lengths.

t is not necessary to provide the particular means illustrated for iine tuning for such tuning may be effected by a removable adjustment device such for example as a nut-like member adapted to be attached to one end of the outer tubular conducto-rand having a bolt-like member threaded therethrough and adapted to engage the piston so that by turning the bolt inthe nut the piston may be iinely adjusted in position. After adjustment has been made, the removable adjustment member would be removed and the piston firmly clamped in its adjusted po-sition. The illustrated arrangement is, however, preferred.

In practice it is intended to use two rejector units in accordance with this invention to reject each undesired harmonic in a transmitter output.

What is claimed is:

1. A tuned circuit arrangement comprising an outer tubular conductor and a second conductor positioned within said outer conductor,` a plurality of fixed condensers in parallel relation connected'between said inner and outer conductors, the efective lengths of said outer and inner conductors determining-the inductance of said tuned circuit, and said plurality of condensers together with a'capacitance existing between said outer and 'inner conductors over their effective lengths determining the capacity of said tuned circuit, and a bridge member slidably mounted with reference to said conductors and conductively contacting both of said conductors, wherebyY the na-tural 'frequency of said tuned circuit can be 'changed-with movement of said bridge member'over said conductors.

2.- VAn-'arrangement as claimed in claim l,

Echaracterized in this that the bridge member comprises a substantially circular arrangement conductively coupling the outer surface of the inner Iconductorand theinner surface of -the outer conductor, and includinga tube surrounding said inner conductor at one -end and connected to said bridge member for adjusting the position ofsaid member with respect to said con-r,

ductors.

3. A tuned circuit arrangement comprising innerand outer concentric conductors, a plurality of condensers in parallel relation coupling together said conductors at one end of said ar-z.

rangement, said condensers being symmetrically located around said inner conductor, a bridge member for adjustablycoupling said conductors together conductively at points along the lengths of said conductors, means for locking said bridgel memberin any desired position along said conductors, and means for obtaining a fine adjustment of the movement of said member, whereby the natural frequency of said tunedcircuit can be changed with movement of said bridgemember over the length of said conductors.

4. A tuned circuit arrangement comprising an outer tubular conductor and a second conductor positioned within said outer conductor, a fixed condenser connected between said inner and. ,l outer conductors, and a bridge member slidablyV mounted with reference to said conductors and adapted to contact with both of them, said bridgevmember being expandible so that it can be expanded to press against the inner and outer n conductors and thus be locked in any desired position of adjustment at the same time giving .good contact with the said conductors, whereby the natural frequency of said tuned circuit can be changed with movement of said bridge mem- 5 0 natural frequency of said tuned circuit can be v changed with movement of saidbridge member' over the length of said conductors.

6. A system in accordance with claim 3, including-an insulating handle and a mechanical link extending from said handle over said inner v lconductor to said bridge member for eiecting said fine adjustment of said bridge member.

DANIEL EDWARD ODONOVAN. 

